A series of well-defined amphiphilic graft copolymers consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic polystyrene side chains were synthesized by hydrolysis of poly(methyl acrylate)-g-polystyrene under basic condition. The backbone and the side chains were synthesized by atom transfer radical polymerization (ATRP), so the molecular weight could be tuned by the variation of the feed ratio or monomer conversion, and the molecular weight distributions of amphiphilic graft copolymers were kept low (PDI < 1.35). The products were characterized by FT-IR, H-1 NMR, C-13 NMR, and gel permeation chromatography (GPC). The study of self-assembly behavior can benefit the formation of the well-defined structures of the products.